Petrochemical products such as oil and gas are ubiquitous in society and can be found in everything from gasoline to children's toys. Because of this, the demand for oil and gas remains high. In order to meet this high demand, it is important to locate oil and gas reserves in the Earth. Scientists and engineers conduct “surveys” utilizing, among other things, seismic and other remote sensing exploration techniques to find oil and gas reservoirs within the Earth, to monitor changes in the subsurface of the Earth caused by drilling, hydraulic fracturing (also known as “fracking”), and other oil and gas extraction techniques, and so forth. By observing the seismic signals detected by one or more seismic sensors or receivers (such as a geophone, accelerometer, hydrophone, etc.) during the survey, the geophysical data pertaining to signals may be used to, for example, help create an image of the subsurface of the earth, to indicate the composition of the subsurface proximate the survey location, to indicate changes in the subsurface, to indicate a location of a seismic source event, and so forth.
Signals recorded in seismic sensors typically contain noise, which may include random noise and/or coherent noise (e.g., trucks driving on the surface of the earth, drilling, etc.). Furthermore, errors in the recording or transmitting equipment, and/or incorrectly sampled data may result in a signal containing undesirable “noise.” To help reduce noise, multiple seismic input traces can be stacked or summed together to create a stacked trace with an improved signal-to-noise ratio. The stacked trace typically represents an improvement as compared with individual seismic input traces, but even the stacked trace can still include noise and may even be unusable without further noise reduction efforts.
As just one example, imaging of passive data in micro-seismic studies typically includes imaging seismic events of relatively small magnitude. The events may be buried in substantial amounts of background noise of various types, which may make it difficult to identify the events. In imaging such data, stacking can help, to some degree, reduce the impact of the noise.
In some circumstances (including passive, micro-seismic studies), there may only be a small number of traces to stack, which typically results in less noise reduction capability. In these cases, noise may overshadow the arrival of the source event in the individual traces, even if stacking is employed. The present disclosure presents a method to reduce the impact of the noise and as such, in some embodiments, improve the ability to image weak events present in passive seismic data studies such as those acquired in micro-seismic monitoring.